It is known that the aromatic polyamide resins exhibit excellent thermal properties, for example, a high melting point and an excellent heat resistance, excellent mechanical properties, for example, a high tenacity and a superior abrasion resistance, and an excellent electric insulating property. Accordingly, the aromatic polymer resins are utilized to produce various filaments, fibers, films, sheets and other shaped articles.
Also, it is known that the high melting points of the aromatic polyamide resins are very close to the corresponding special temperatures at which the aromatic polyamide resins are decomposed thermally. Due to this property, usually, it is practically impossible to shape the aromatic polyamide resins by means of a melt-shaping process. Accordingly, in order to produce the shaped articles, such as filaments, films and sheets, from the aromatic polyamide resins, in general, the aromatic polyamide resins are dissolved in a concentration of from 5 to 20% in an organic polar solvent, for instance, dimethyl formamide, N-methyl-2-pyrrolidone and dimethyl acetamide, and the solution is extruded through at least one nozzle, die or orifice into a wet coagulating bath or a dry solidifying atmosphere, so as to eliminate the solvent from the extruded solution. That is, in general, the production of the shaped aromatic polyamide resin articles is carried out by the so-called wet-shaping process or dry-shaping process.
However, in the above-mentioned comventional shaping processes, a large amount of the organic polar solvent, which is expensive, is used to prepare the solution of the aromatic polyamide resin, and also, a large amount of other organic solvent is used to recover the organic polar solvent. The use of the large amount of the organic polar solvent and the recovering solvent results in a high cost of the shaping process of the aromatic polyamide resin articles.
Furthermore, it is known that, in spite of the fact that the expensive polar solvent is used in a large amount, the shaping property, for example, spinning property and film-forming property, of the conventional aromatic polyamide composition is not always satisfactory.
Under these circumstances, it is strongly desired to provide an aromatic polyamide composition which comprises a relatively cheap solvent in a relatively small amount and which has an enhanced shaping property.
For the purpose of attaining the above-mentioned desire, attempts were made to use a solution of the aromatic polyamide resin in a high concentration, in the shaping process of the aromatic polyamide articles. This solution is effective for reducing the consumption of the expensive polar solvent and, thus, for minimizing the cost of the shaping process. However, some of the aromatic polyamide resin, for example, m-phenylene isophthalamide unit-containing polyamides which are most popular and most useful for producing the shaped articles, exhibit a special tendency to crystallize and become insoluble in the polar solvent when the concentration of the aromatic polyamide in the solution is about 23% by weight or more and the temperature of the solution is 80.degree. C. or more. That is, at the above-mentioned temperature and in the above-mentioned concentration, the aromatic polyamide is deposited in the form of crystals from the solution. The above-mentioned high concentration of the solution cannot be utilized in the shaping process.
Each of Japanese Patent Applications Laying-open Nos. 52-13545, 52-15675, 52-53068, 52-98764 and 52-101298 discloses a method in which the m-phenylene isophthalamide unit-containing polyamide resin is completely dissolved in an excessive amount of the polar solvent selected from N-methyl-2-pyrrolidone, hexamethyl phosphoramide, 2-pyrrolidone and .epsilon.-caprolactam, and; then, the excessive amount of the polar solvent is evaporated away from the solution by heating the solution at an elevated temperature, under a reduced pressure, so as to provide a crystalline complex of the polyamide and the polar solvent. However, the above-mentioned process for producing the crystalline complex exhibits the following disadvantages.
1. Since the polar solvent is used in a larger amount than that of the conventional method, this method cannot attain the desire of reducing the consumption of the polar solvent.
2. The evaporative operation of the polar solvent from the solution requires a large amount of energy and labor.
3. The crystalline complex of the polyamide resin and the polar solvent is stable only at a low temperature and for a short time from the its preparation. Therefore, it is difficult to utilize the crystalline complex in the shaping process at an elevated temperature. Usually, the crystalline complex connot be used in an industrial shaping process.